Effect of Foliar Application of GA₃, NAA, and Zinc on Growth, Yield, and Quality of Onion (Allium cepa L.)

Abstract

Onion (Allium cepa L.) is an economically important vegetable crop valued for its culinary, nutritional, and commercial significance. Optimising the foliar application of plant growth regulators and micronutrients may improve onion growth, bulb yield, quality, and production economics. The study aims to evaluate the effects of plant growth regulators and zinc on the growth, yield, and quality of onion. A field experiment was conducted during the rabi season of 2025–26 at the Horticulture Research Field, Prof. Rajendra Singh (Rajju Bhaiya) University, Naini, Prayagraj, Uttar Pradesh, The experiment was arranged in a randomised block design with seven treatments and three replications. The treatments comprised GA₃ (100 ppm), NAA (200 ppm), zinc (0.1%), and their combinations, applied as foliar sprays at 30 and 60 days after transplanting (DAT). Among the treatments, T₅ (GA₃ 100 ppm + zinc 0.1%) produced the highest plant height (56.57, 60.12, and 66.19 cm), number of leaves per plant (6.87, 8.00, and 13.01), pseudostem length (6.83, 9.32, and 14.74 cm), and pseudostem diameter (1.92, 2.83, and 3.51 cm) at 45, 60, and 90 DAT, respectively. The same treatment also recorded the highest average bulb weight (85.36 g), polar diameter (6.14 cm), equatorial diameter (6.33 cm), yield per plot (11.35 kg plot⁻¹), and yield per hectare (28.38 t ha⁻¹), followed by T₆ (NAA 200 ppm + zinc 0.1%). In contrast, the highest total soluble solids (12.20 °Brix), titratable acidity (0.31%), ascorbic acid (13.43 mg 100 g⁻¹), and total sugar content (6.43%) were recorded under T₄ (GA₃ 100 ppm + NAA 200 ppm). The control (T₇) recorded the lowest values for most parameters. In this study, GA₃ (100 ppm) combined with zinc (0.1%) improved onion growth and yield, whereas GA₃ (100 ppm) combined with NAA (200 ppm) improved bulb quality.